Piles used as foundation elements for support structures of offshore wind energy converters (OWECs) are subject to highly cyclic tension or compressive loading. It is known from a number of field and model tests that piles under cyclic axial loading can exhibit a significant reduction of capacity compared to the static loading case. Interaction diagrams have been developed, which give the number of load cycles leading to failure dependent on the mean load and the amplitude of the cyclic load portion, both related to the static capacity. However, such diagrams cannot account for soil conditions or pile geometry. A generally valid calculation approach is not yet available. In this paper a numerical simulation scheme applicable to sandy soil is presented, which allows developing interaction diagrams for arbitrary pile dimensions. The calculation results for two piles with different dimensions in sand under one-way cyclic loading in tension are presented and compared to existing interaction diagrams.